Magneto-rheological steering damper

ABSTRACT

A vibration damper assembly to dampen the vibration generated in a motor vehicle and transmitted through, for example, a steering assembly. The vibration damper assembly includes a rotor disposed within a housing. The rotor is operatively connected to a velocity generating member such as a pinion that is integrated with the steering assembly. A conductive sleeve is disposed between the housing and the rotor. A coil engages the sleeve and is capable of generating a magnetic field that is transmitted through the sleeve. A plate separates the rotor from the sleeve thereby defining a viscous fluid chamber and a Magneto-Rheological (MR) fluid chamber between the rotor and the sleeve. The viscous fluid chamber includes a Newtonian fluid and the MR fluid chamber includes a MR fluid having sheer properties reactive to the magnetic field.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional PatentApplication Serial No. 60/245,979, filed Nov. 3, 2000.

TECHNICAL FIELD

[0002] The subject invention relates generally to vibration damping ofsuspension and steering systems in a motor vehicle. More specifically,the subject invention relates to vibration damping using viscous sheerand magneto-rheological clutching.

BACKGROUND OF THE INVENTION

[0003] Rotary dampers have been installed in both steering andsuspension assemblies of motor vehicles to dampen the amount ofvibration detected by the vehicle operator from such variables asvehicle speed, road bumps, wheel alignment, wheel chatter, and treadwear. Rotary dampers of this type reduce the amount of vibrationtransferred to the vehicle operator by resisting rotational velocitygenerated from a pinion associated with either the steering assembly orthe suspension assembly. The rotational velocity is resisted by torquegenerated by the rotary damper thereby reducing vibration. The torque isderived from a clutch-like resistance generated by a fluid, having aNewtonian behavior, when a rotor disposed within the vibration damperassembly is operatively connected to the pinion and receives rotationalvelocity from the pinion.

[0004] The rotational velocity generated by the pinion connected to therotary damper varies with the amount of vibration absorbed from theoperating variables listed above. A different level of torque isrequired to provide uniform dampening at high rotational velocities thanat low rotational velocities. A Newtonian fluid provides adequate torqueat low rotational velocity, however, at high rotational velocities, toomuch torque is provided by the Newtonian fluid, which reduces theeffectiveness of the rotary damper.

[0005] Therefore, it would be desirable to provide a rotary damperhaving variable torque capabilities that would optimize the amount ofvibration damping at both low and high rotational velocity.

SUMMARY OF THE INVENTION

[0006] The present invention discloses a vibration damper assembly forreducing the amount of vibration transferred to a motor vehicle operatorfrom variables such as vehicle speed, road bumps, wheel alignment, wheelchatter, and tread wear.

[0007] The assembly includes a rotor disposed within a housing. Therotor is operatively connected to a rotational velocity generatingmember, such as a pinion, that is connected to a steering or suspensionassembly. A conductive sleeve is positioned between the housing and therotor. A coil is positioned adjacent the sleeve and is capable ofgenerating a magnetic field that is transmitted through the sleeve. Anannular plate separates the rotor from the sleeve and defines a viscouschamber and a Magneto-Rheological (MR) fluid chamber. The viscouschamber is disposed between the sleeve and the housing and the MRchamber is disposed between the sleeve and the rotor. A viscous fluid iscontained within the viscous chamber and an MR fluid is contained withinthe MR chamber. The viscous fluid behaves as a Newtonian fluidthroughout operation of the assembly. The MR fluid behaves as a Binghamplastic when it is subjected to the magnetic field and otherwise,behaves as a Newtonian fluid.

[0008] The subject concept overcomes the deficiencies of the prior artby providing the ability to vary the amount of torque generated by thevibration damper assembly. When not subjected to the magnetic field, thetorque is generated by a Newtonian fluid, which is preferable at lowvelocity. When subjected to the magnetic field, the MR fluid istransformed from a fluid having Newtonian characteristic to a fluidhaving Bingham plastic characteristics, which generates a torque that ispreferable at higher velocities.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a sectional view of the vibration damper assembly of thepresent invention;

[0010]FIG. 2 is a sectional view of an alternative embodiment of thevibration damper assembly of the present invention;

[0011]FIG. 3 is an exploded view of the vibration damper assembly of thepresent invention;

[0012]FIG. 4 is perspective view of a rack and pinion steering assemblyshowing the vibration damper assembly of the present;

[0013]FIG. 5 is a graph showing the relation between torque and velocityfor the fluids used in the vibration damper assembly; and

[0014]FIG. 6 is a sectional view of an alternative embodiment of thevibration damper assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0015] Referring to FIG. 1, a vibration damper assembly is generallyshown at 10. The assembly 10 utilizes magneto-rheological fluid incombination with a Newtonian fluid to reduce the vibration associatedwith, for example, rack and pinion steering systems commonly installedin motor vehicles. The assembly 10 can also be installed in othersystems, such as, for example a vehicle suspension system.

[0016] A rotor 12 is centrally located within an assembly housing 14.The rotor 12 includes a spline 16 for receiving a distal end of a pinion18 from a steering gear 20 (FIG. 4). Alternatively, as shown in FIG. 2,the rotor 12 can include a shaft 21 for engaging a steering pinion. Afirst plurality of bearing assemblies 22 and a second plurality ofbearing assemblies 23 align the rotor 12 inside the housing 14 allowingthe rotor 12 to pivot with the pinion relative to the housing 14.

[0017] A first polar ring 24 and a second polar ring 26 are positionedbetween the housing 14 and the rotor 12. The first polar ring 24 abutsthe first plurality of bearings 22 but does not interfere with theinteraction between the first plurality of bearings 22, with the rotor12 and the housing 14. The second polar ring 26 protrudes through thehousing 14 at an end opposite the spline 16. The polar rings 24, 26 arepreferably formed from an annealed mild steel and readily conductmagnetic fields. The second plurality of bearings 23 is positionedbetween the second polar ring 26 and the rotor 12 allowing the rotor 12to pivot with the spline 16 relative to the second polar ring 26. Thefirst polar ring 24 does not contact the rotor and therefore does notrequire any bearings to separate it from the rotor 12 as will be furtherevident below.

[0018] A non-magnetic insert 30 connects the first polar ring 24 to thesecond polar ring 26 forming a sleeve capable of conducting separatemagnetic fields. The preferable method for connecting the non-magneticinsert 30 to the polar rings 24, 26 is by brazing. However, othermethods of connection may be used if desired. The non-magnetic insert 30insulates each polar ring 24, 26 from the other. Therefore, the firstpolar ring 24 can have a different magnetic potential than the secondpolar ring 26 depending upon the direction of a magnetic fieldcontacting each of the rings 24, 26.

[0019] A coil 32 overlays the non-magnetic insert 30 and contacts boththe first and second polar rings 24, 26. The coil 32 is attached to anelectrical connector 34. When receiving an electrical current via theelectrical connector 34 the coil 32 generates a magnetic field M. Asrepresented in FIG. 1, the magnet field M travels in differentdirections through each of the polar rings 24, 26. The magnetic field Mtherefore magnetizes one of the polar rings 24, 26 with a Northern biasand the other of the polar rings 24, 26 with a Southern bias. Becausethe non-magnetic insert 30 insulates the first polar ring 24 from thesecond polar ring 26 different poles are established in each polar ring24, 26.

[0020] A sleeve 36 encircles the rotor 12 between the bearings 22, 28.The sleeve 36 is positioned between the rotor 12 and the first andsecond polar rings 24, 26 forming an inner chamber 38 with the rotor 12and an outer chamber 40 with the polar rings 24, 26. The sleeve 36 mayinclude magnetic or non-magnetic properties depending upon the strengthrequirements of the magnetic field M. If a low level magnetic field isrequired, a non-magnetic sleeve is utilized. If a high level magneticfield is required, a conductive sleeve is utilized. Amagneto-rheological (MR) fluid fills the inner chamber 38 and a viscousfluid fills the outer chamber 40.

[0021] The sleeve 36 is centered between upper and lower outer seals 42and upper and lower inner seals 44. The outer seals 42 retain theviscous fluid in the outer chamber 40 and the inner seals retain the MRfluid in the inner chamber 38. A plug 46 seals an aperture 48 (FIG. 3)in the rotor 12 to prevent the assembly 10 components from beingcontaminated from environmental elements.

[0022] The MR fluid retains Newtonian shear characteristic when notsubjected to the magnetic field M. The viscous fluid retains Newtonianproperties throughout operation of the assembly 10. When subjected tothe magnetic field M generated by the coil 32, the yield stress of theMR fluid increases and stabilizes establishing sheer characteristics ofa Bingham plastic.

[0023] Referring to FIG. 4, rotational velocity is generated by thepinion 18, and transferred to the rotor 12, by a number of differentvehicle operating variables. The variables include vehicle speed, roadbumps, wheel alignment, wheel chatter, tread wear and others. Therotational velocity is transferred through the steering column (notshown) to the driver in the form of vibration when the rotationalvelocity is not damped. The assembly 10 uses torque generated by viscousand sheer forces between the rotor 12, the sleeve 36 and the polar rings24, 26 to damp the vibration. Resistance to the rotational velocity ofthe rotor 12 in the form of torque is generated from the MR and viscousfluids.

[0024] The rotation resisting torque generated in the rotor 12 dampensthe vibrations derived from the rotational velocity of the pinion 18.The resisting torque generated by each fluid is applied to the otherfluid so that the lesser torque is the effective torque of the assembly10. When the coil 32 is not energized, the MR fluid generates a torquein the inner chamber 38 low enough to allow the rotor 12 to turn freely.When the coil 32 is energized, the torque generated in the assembly 10is a combination of both the viscous fluid and the MR fluid as shown inFIG. 5. At low velocity, the torque generated is primarily from theviscous fluid and, therefore, follows the viscous curve. At highervelocities, the magnetic field is energized. Thus, the torque generatedis primarily from the MR fluid, and, therefore, follows the MR curve.If, at high velocities, the viscous fluid generates the entire torque,an unfavorable high level of motion would be generated allowingvibration to be transferred through the steering column. By activatingthe MR fluid at high velocities, a more uniform level of damping isachieved.

[0025]FIG. 6 shows an alternative embodiment as a plate style damperassembly generally at 40. A plate rotor 42 receives a pinion (not shown)with a spline 44. A conductive core 47 protrudes through a housing 48that encloses the components of the assembly 40. Disposed within thecore 46 is an electric coil 50, which when conducting electricitygenerates a magnetic field represented as M. A plate 52 is positionedbetween the plate rotor 42 and the magnetic core 46 forming a firstchamber 54 and a second chamber 56. Viscous (Newtonian) fluid isdisposed within the first chamber 54 and MR fluid is disposed within thesecond chamber 56. A spacer 58 separates the plate 52 from theconductive core 46 to maintain enough space in the first chamber 54 tohold the viscous fluid.

[0026] A core O-ring 60 seals the viscous fluid inside the upper chamber54. A first and second rotor O-ring 62, 64 seal the MR fluid insidelower chamber 56. A plurality of bearings 66 position the plate rotor 42within the housing 48 allowing the rotor 42 and the pinion to rotaterelative to the housing 48. The plate 52 is made of a magnetically inertmaterial, such as, for example stainless steel.

[0027] The plate style damper assembly 40 operates much the same as thepreferred embodiment (assembly 10). When the coil 50 is not energized,the MR fluid provides relatively little torque to the rotation of therotor 46. When the coil 50 is energized, the combination of the viscousfluid and the MR fluid provides low damping at lower rotational velocityand damping that levels off at higher rotational velocity as is shown bythe curve in FIG. 5.

1. A vibration damping assembly comprising: a housing; a rotor disposedwithin said housing operatively connected to a rotation generatingmember; a panel with conductive properties positioned adjacent saidrotor; a coil circumscribing said panel and being capable of carrying anelectric current thereby generating a magnetic field through said panel;a separating member positioned between said rotor and said paneldefining a viscous fluid chamber and a magneto-rheological (MR) fluidchamber between said rotor and said panel wherein viscous fluid isdisposed within said viscous fluid chamber and MR fluid is disposedwithin said MR chamber, said MR fluid having sheer properties reactiveto said magnetic field generated by said coil.
 2. An assembly as setforth in claim 1 further including a plurality of bearings disposedbetween said rotor and said housing allowing said rotor to rotaterelative to said housing.
 3. An assembly as set forth in claim 1 whereinsaid panel includes a non-magnetic insert defining a first polar ringand a second polar ring within said panel.
 4. An assembly as set forthin claim 3 wherein said magnetic field generates a first polar bias insaid first polar ring and a second polar bias in said second polar ring.5. An assembly as set forth in claim 4 wherein said coil is positionedadjacent said non-magnetic member.
 6. An assembly as set forth in claim1 wherein said coil includes an electrical connector connecting saidcoil to a source of electicity.
 7. An assembly as set forth in claim 1including a pair of outer seals and a pair of inner seals sealing saidMR fluid within said MR chamber and said viscous fluid within saidviscous chamber.
 8. An assembly as set forth in claim 1 wherein saidviscous fluid includes Newtonian sheer properties
 9. An assembly as setforth in claim 1 wherein in said coil receives electrical current whensaid rotor includes a high rotational velocity thereby providingvibration damping torque characteristic of said MR fluid.
 10. Anassembly as set forth in claim 1 wherein said coil does not receiveelectrical current when said rotor includes a low rotational velocitythereby providing vibration damping torque characteristic of saidviscous fluid having Newtonian sheer properties.
 11. An assembly as setforth in claim 1 wherein said separating member comprises a sleevecircumscribing said rotor.
 12. An assembly as set forth in claim 1wherein said separating member comprises a plate having a generally flatprofile and being positioned between said rotor and said panel.
 13. Anassembly as set forth in claim 12 wherein said panel comprises a corewith conductive properties and having said coil disposed therein.
 14. Amethod of damping vibration transmitted through steering and suspensionsystem of an automobile comprising the steps of: affixing a rotarydamper capable of damping vibration by generating torque to resistrotational movement to a pinion; detecting rotational velocity of saidpinion; generating torque from a fluid having Newtonian sheercharacteristics during a first rotational velocity range of said pinion;generating torque from a fluid having non-Newtonian sheercharacteristics during a second rotational velocity range of saidpinion.
 15. A method as set forth in claim 14 wherein said step ofgenerating torque from a fluid having non-Newtonian sheercharacteristics is further defined as generating a torque from a fluidhaving a Bingham plastic sheer characteristic.
 16. A method as set forthin claim 14 further including the step of magnetizing said non-Newtonianfluid during a second rotational velocity range of said pinion therebychanging the sheer properties of the non-Newtonian fluid from beingcharacteristic of a Newtonian fluid to being characteristic of a Binghamplastic.
 17. A method as set forth in claim 14 further including thestep of energizing a coil disposed within said rotary damper therebygenerating said magnetic field upon said MR fluid.
 18. A method a setforth in claim 17 further including the step of de-energizing said coildisposed within said rotary damper thereby terminating said magneticfield being emitted upon said MR fluid.